Water diffusion in additively manufactured PETG: Microstructure-based modelling

Additive manufacturing (AM) is an advanced manufacturing method that produces objects by sequential layering. AM with continuous-fibre reinforcement is becoming more widely used in various fields such as aerospace, biomedical, and motorsport. The use of carbon-fibre-reinforced polymers (CFRP) in shipbuilding, where structures are exposed to the marine environment, is also increasing. However, the water-diffusion process and the effect of water ageing on the mechanical performance of AM materials is not yet well understood due to their complex internal structure, caused by defects during manufacturing. Current research on diffusion is mostly based on experimental methods for conventionally manufactured materials without considering AM-induced defects. The objective of this study is to model a water-diffusion process in AM materials using microstructural data, acquired with optical microscopy. The obtained micrographs were segmented to mitigate the influence of the random distribution of fibres and defects in the composite material. The segmented images were then binarised and the volume fractions of fibres and voids were evaluated employing a pixel-based approach in Python. This information was used to build a finite-element model in the finite-element software Abaqus. The developed model is based on the mass diffusion analysis following Fick’s law and was used to compare the water uptake performance of a pure matrix, a single fibre, a fibre cluster and a periodic array of fibres. The simulation results demonstrate that the internal structure of AM composite materials has a significant influence on water diffusivity compared to their conventionally manufactured analogues.